Large organizational tree structures often cannot be easily visualized by means of regular graphical tree layouts because the graph soon becomes too large due to the overloading of information on the screen. Indeed, displaying just a few hundred edges on a regular screen window makes the picture unreadable.
Multiple solutions have been proposed in the past that enabled a user to see only portions of a graph (via a zoom in window for instance) such as the hyperbolic tree model from Xerox (registered trademark), or even drastically different models such as the University of MarylandAEs tree maps by Johnson and Shneiderman. These solutions only bring partial answers either because they are difficult to interact with (the zoom in window can be difficult to position on a portion of graph with a very large branching factor), to visualize (while extremely intuitive, the hyperbolic scheme raises the same problem as the zoom), or are simply difficult to understand for the user insofar as the tree map view requires a significant amount of learning time as explained by the authors themselves.
Pragmatically, the standard tree-control view familiar to Personal Computer (PC) users, for example the Windows (registered trademark) 95/NT (registered trademark) Explorer and multiple applications on Windows (Registered trademark), in which the tree is represented as a hierarchy of folders is the most widespread and the most intuitive as it can support arbitrarily long lists of descendants for any node, via the scrollbar mechanism of the window. However, such a system is basically line-based and not graphical and also lacks aesthetic quality. More graphical layouts in which siblings are on a same axis and connected to their direct parent by a straight line do not scale up.